Hydraulic free-wheeling means for the hydraulic drives of conveyors and the like



e/llcL INVENTOR )IARRY RUSENBERG HYDRAULIC FREE-WHEELING MEANS FOR THEHYDRAULIC` DRIVES OF CONVEYORS AND THE LIKE Dec. 10, 1968 United StatesPatent O 31 10 Claims. (Cl. 60-53) ABSTRACT F THE DISCLOSURE Hydraulicdrive arrangement including hydraulic drive means having `main workingiiow line means and main return ow line means operatively How-connectedtherewith for hydraulic actuation thereof, short-circuit ow line meansdisposed correspondingly in such short-circuit ow return ilow line meansto bypass such drive imeans, a pair of independently openableoperatively opposed check valve means disposed correspondingly in suchshort-circuit flow line `means to permit when open short-circuit bypassilow therethrough, and control means operatively connected with suchcheck valve means to open the check valve means independently of oneanother, such control means including, for example, hydraulic controlvalve means and control flow line means operatively ow connecting thecontrol valve rneans with the check valve means to open hydraulicallyeach check valve means independently, the control valve `means beingImanually or automatically operable.

The present invention relates to hydraulic drive arrangements, and 4moreparticularly to such arrangements coritemplating free-wheeling meanswhereby to achieve under varying pressure conditions free-wheeling ofthe hydraulic drive system especially in connection with multi-motorhydraulic drives for conveyors, and the like.

In hydraulic drives of the kind in question, especially where a pair ofsuch drives is used for driving a conveyor system, one such drive maysometimes practically overtake the other. In the motor or drive that isovertaken in speed, a reversal of its function is produced in that itoperates `as a pump since both drives are coupled together by thehydraulic fluid system utilized. In particular, such hydraulic drivesare provided in the form of rotary vane machines or rotary pistonmachines, i.e. rotary iluid machines, which transmit hydraulic powerinto mechanical l power in one direction of operation (performing as amotor) `and mechanical ypower into hydraulic power in the otherdirection of operation (performing as a pump). In connection with theforegoing, as a result of the overtaking of one such hydraulic drive bythe other, a drop in pressure develops in the pressure output lineunless the hydraulic drive acting as a pump is able to put out suicientiluid -to make up the deficiency. More precisely, the input pressure ofthe overtaken hydraulic drive is reduced to the level of the outputpressure thereof, and thereafter the above-noted eifect takes placewhereupon the output pressure exceeds the input pressure. In the extremecase the faster running drive means may use up all its power in draggingalong the slower running drive means since the latter acts as a pumprather than `a motor.

3,415,057 Patented lDec. 10, 1968 ice It is true that the foregoingdisadvantageous eifect can be mitigated -by the use of known powerregulators or governors customarily employed for such purposes.Nevertheless, a -certain energy loss will result because of thenecessity of balancing the speed of the two or more hydraulic drivemeans operatively coupled together, for example, with a conveyor systemto be driven thereby. Specifically, such energy losses will occur in anycase until the threshold response pressure of the power regulatorassociated with the faster running drive is reached` However, at extremeloads, a reciprocal build-up of counter-pressures in the drive means maybe produced by oscillating effects in the endless conveyor chain or beltsystem and/ or by diiierent speeds of response of the power valvesnecessary for the hydraulic energizing of the two or more drive means.Only at no-load speeds which are very accurately attuned to one anotheras between the two or more drive means utilized, and only when suchdrive means have the same characteristic with respect 'to the deliveryrate, and furthermore operate with approximately equal losses and/ oreiciency, can quick balancing of the speeds be achieved. In practice,this set of conditions is seldom attained and, therefore, the problem ofovertake with respect to two or more hydraulic iluid operated drivemachines, or the like, arranged for conjoint output at the same speedcannot be overcome.

It is an object of the present invention to overcome the foregoingdrawbacks and to provide hydraulic drive arrangements for use inconjoint operation of a co-mmon drivable system to be driven therebywithout overtake in speed of one drive means with respect to the other.

It is another object of the present invention to provide `an arrangementof the `foregoing type in which hydraulic free-wheeling means areincluded whereby to achieve under varying pressure conditionsfree-wheeling of the hydraulic drive system especially in connectionwith `multimotor hydraulic drives for conveyors, and the like.

It is a further object of the present invention to provide anarrangement of the foregoing type with respect to a given rotary fluidmachine wherein the hydraulic input line to such `machine and thehydraulic output line from such machine are provided with aIfree-wheeling system or neutral operating condition system analogous tothat applied heretofore in mechanical drives, whereby a shortcircuitcycle connection between such input and output lines is employedtogether with control means for permitting pressure flow communicationbetween such inlet and outlet lines to equalize the pressuretherebetween and thus permit an idle or neutral condition of operationto exist with respect to such drive and thereby avoid energy loss in asecond such drive means operated conjointly therewith at a diierentspeed.

It is a still further object to provide only one such arrangement, e.g.where such drive must avoid operating as a brake for its associateddrivable system.

Other and further objects of the present invention will become apparentfrom :a study of the within specification and accompanying drawings inwhich the figure shown illustrates schematically an arrangement of twosuch hydraulic drive means conjointly arranged for driving an endlessconveyor system, with each such hydraulic drive means having ashort-circuit ow system provided between the corresponding inlet `andoutlet flow lines thereof, in accordance with the present invention.

It has been found in accordance with the present invention that ahydraulic drive arrangement may now be provided to overcome theforegoing disadvantages. Such arrangement comprises hydraulic drivemeans having main working ow line means and main return ow line meansoperatively dow-connected therewith for the hydraulic actuation thereof,short-circuit flow line means correspondingly interconnecting saidworking and return flow line means to by-pass said drive means, a pairof independently openable operatively opposed check valve means disposedcorrespondingly in said short-circuit flow line means to per-mit whenopened short-circuit by-pass ilow therethrough, and control meansoperatively connected with said check valve means to open said checkvalve means independently of one another.

Preferably, the control means include hydraulic control v alve `meansand control flow line means operatively flow-connecting said controlvalve means with said check valve means .to open hydraulically eachcheck valve means independently. Such control valve means may bemanually operable or automatically operated in conjunction with aprogrammed system.

In accordance with one specic feature of the present invention, at leasttwo separate hydraulic drive means of the foregoing type are provided inindependent operative association with a common drivable system to bedriven cooperatively the-reby, each said drive means having a separateset of said working land return flow line means operativelyHow-connected therewith and a separate said short-circuit ow line meanscorrespondingly interconnecting said working and return flow line meansto bypass the particular drive means as well as a pair of said checkvalve means disposed correspondingly in the particular short-circuit owline means, with said control means being operatively connected withsaid check valve means to open said check valve means independently ofone another. In this regard, each pair of check valve means is providedpreferably with a separate control means operated independently of theother.

The hydraulic drive -means in each case may conveniently take the formof a hydraulically operated rotary drive machine and the com-mondrivable system may be a conveyor system such as a chain scraperconveyor system utilized in mining operations, or a mining planertraction cable, etc.

Advantageously, the pair of check valve means should be disposed inseries flow relation in the short-circuit How line means and normallymaintained closed by .the corresponding normally existing positivehydraulic pressure exerted thereagainst through the appropriate m-ain owline means and the corresponding portion of said shortcircuit flow linemeans flow-communicating therewith.

Referring to the drawing, the figure illustrates diagrammatically ahydraulic drive system, for use with an endless conveying chain, belt,or the like, which may be, for example, the chain used to drive a miningmachine, such as a coal planer, back and forth along a mine face or ascraper chain of a mining conveyor used to convey mineral, such as coal,away from the site of mineral winning from a mine Iface. Such miningmachines and mining conveyors are normally used in longwall miningoperations, such as in the winning of coal.

Conveyor 1 which may take the form of a conveyor belt is mounted on apair of spaced apart driving wheels or drums 2, 3 which are coupled viathe corresponding clutches 4, 5 with the appropriate hydraulic drive 6,as the case may be.

Such hydraulic drive 6 may be in the form of a rotary fluid machinenormally disposed to function as a hydraulic motor under positivehydraulic pressure provided through the hydraulic system 7 in eachinstance.

Describing the operation of the hydraulic system 7 used to drive thehydraulic motor 6 coupled via clutch 4 with drum 2, it will be seen thatthe main working ilow line 8 under hydraulic pressure generated by pumpCil 10 or similar means is fed to the motor 6 to cause such motor torotate and thus transmit lrotary motion via clutch 4 to drum 2 to causein turn travel of endless conveyor 1 in the direction shown by thearrow. The spent hydraulic fluid passes via the main return flow line 9back to the pump 1li or the like. Pump 10 is normally positioned at aconvenient distance from motor 6 and the main flow lines 8 and 9 may beof any appropriate length. Pump 10 may be replaced by other means whichwill provide under normal operation a higher working pressure in line 8than in line 9, yet the pressure in lines 8 and 9 will normally bepositive pressure.

In accordance with the present invention, the main flow lines S and 9are interconnected by means of a by-pass or short-circuit line 11 inwhich are disposed in series flow connection the operatively opposedcheck valves 12 and 13. Check valves 12 and 13 may be of any convenientdesign which permit under normal operation unilateral back low when thevalve body 12a or 13a is displaced away from the valve seat 12b or 13b,as the case may be. Thus, when valve body 12a is displaced from valveseat 12b, the working pressure in line 8 will be exerted upon valve body13a to force such valve body away from the valve seat 13b. In the sameway, when valve body 13a is displaced from valve seat 13b, the workingpressure in line 9 will be exerted upon valve body 12a to force suchvalve body away from the valve seat 12b. In accordance with the presentinvention, the displacing of valve body 12a and valve body 13a away fromthe appropriate valve seat is carried out by auxiliary control means 16.Auxiliary control means 16 may take the form of an auxiliary hydraulicuid system, including control flow line 14 to one side 11a of the checkcylinder 11C containing the check piston 11d with the ram 11eoperatively positioned at valve body 12a of check valve 12 and controlline 1S to the other side 11b of the check cylinder 11e` with the otherpiston ram 11f operatively positioned at valve body 13a of check valve13, coupled with the control valve 17, the portion of short-circuit line11 between valve seats 12b and 13b being shown in dash line and actuallyhow-connecting valves 12 and 13. Because of their length, rams 11e and11f when piston 11d is in idle or neutral position will not preventvalve body 12a nor valve body 13a from normal closed seating againstvalve seats 12b and 13b respectively but will only disturb thisrelationship when piston 11d is actuated to the left or right. Controlvalve 17 is connectable to a source (not shown) of hydraulic fluid, or`the like, via the pressure line 18 and via the return line 19. Valve 17is provided with three possible valve positions 20, 21 and 22. Valve 17is displaceable laterally against the spring force of springs 23 and 24which normally maintain valve 17 in the neutral or idle position 20which permits flow communication between control lines 14 and 15. Duringthe normal operation of motor 6, the pressure in line 8 willunderstandably be higher than the pressure in line 9, and the pressurein both main lines 8 and 9 will be positive pressure sufficient tomaintain valve bodies 12a and 13a in closed position against valve seats12b and 13b, as the case may be. During this time, the pressure incontrol lines 14 and 15 will not operate to change the closeddisposition of check valves 12 and 13. Upon displacement of valve 17 tothe right as viewed in the drawing so that valve position 22 is alignedwith the pressure and return lines 18 and 19, the pressure in line 18communicates with control line 14 to cause valve body 13a to bedisplaced away rom valve seat 13b, thus opening check valve 13.

Even so, since the pressure in line 8 is normally higher than that inline 9, the pressure exerted through shortcircuit line 11 via line 9 andvalve 13 will not be suflicient to displace the valve body 12a fromvalve seat 12b. However, upon change in the pressure condition in thehydraulic system 7 such that the pressure in line 9 exceeds that in line8, when valve 17 is in position 22, excess pressure in line 9 will beshort-circuited through line 11 to cause valve body 12a to be displacedas aforesaid, whereupon the pressure in line 8 and line 9 will beeqpalized. Under such conditions, motor 6 will be in freewheeling orneutral or idle position despite the working pressure of pump 10.

On the other hand, upon displacing valve 17 in a direction toward theleft as shown in the drawing to the position 21, then pressure line 18will communicate with control line and return line 19 will communicatewith control line 14. In this instance, the opposite actuation will takeplace, i.e. the hydraulic pressure through line 18 and control line 15will displace valve body 12a from valve seat 12b to open check valve 12.Thence, the pressure in line 8 when the same exceeds that in line 9 willcause the displacement of valve body 13a from valve seat 13b to efrectthe opening of check valve 13 and the equalization of the pressure inline 8 and line 9 as aforesaid.

It will be appreciated that under a versatile arrangement as may beprovided in accordance with the present invention, pump 10 or the likemay be reversed in its operation to provide higher pressure in line 8than in line 9, or higher pressure in line 9 than in line 8. When thepressure in line 8 is higher, then motor 6 will rotate in clockwisedirection whereas when the pressure in line 9 is higher, then motor 6will rotate in icounterclockwise direction, In this way, advantageously,the appropriate rotary motion may be exerted via clutch 4 to drum 2 torotate such drum in the appropriate direction so as to cause the travelin turn of the conveyor 1 in the appropriate direction. This isespecially applicable to the operating of a mining machine, such as amining planer, back and forth along a mine face reciprocally. Forexample, drum 2 may be located at one end of the portion of the mineface being worked and drum 3 at the other end of the portion thereof andby appropriately changing the direction of pressure flow through thepumps 10, or the like, in both arrangements 7, the two motors 6 mayfirst operate in clockwise direction and thence in counterclockwisedirection to achieve the reciprocal movement of the conveyor 1 which maybe a cable to be attached to the mining machine to be reciprocated alongthe mine face.

Of course, the construction and operation of the hydraulic system 7associated with that motor 6 coupled with clutch 5 to transmit rotarymotion to drum 3 will be the same as that described hereinabove inconnection with the imparting of rotary motion in the 'desired directionto drum 2.

In normal operation, both motors 6 are meant to rotate in the samefunctional direction to cause rotary motion to be transmitted throughclutches 4 and 5 to the appropriate drums 2 and 3 so as to attain aconjoint additive rotation of such drums under the combined power ofboth motors 6. In practical operation, however, both motors 6 do notalways rotate the appropriate drums at the exact same speed underapproximately the same efficiency and, therefore, one motor 6 mayovertake the other and cause the corresponding drum of the overtakingmotor to rotate at a higher speed than the other drum. Assuming, forinstance, that motor 6 coupled via clutch 5 to drum 3 operates at ahigher speed than the motor 6 coupled through clutch 4 to drum 2, thenthe latter motor will eventually be dragged along in its functionaloperation because of the conjoint connection of the motor outputs viathe conveyor 1. This will mean that the dragging motor 6 associated withdrum 2 will be rotated via the connection provided by conveyor 1, drum2, and clutch 4, faster than the pressure in line 8 of its hydraulicsystem 7 would normally operate such motor. As a result, hydraulic fluidis taken from the ycorresponding line 8 into the dragging motor 6 underan induced suction and discharged into the corresponding line 9 under ahigher pressure than the normal pressure, causing the dragging motor 6to act as a pump rather than a motor. If, in accordance with the presentinvention, control valve 17 is in position 22 which will serve tomaintain check valve 13 open, then such excess pressure in line 9 willbe short-circuited through line 11 to cause check valve 12 to open inthe above-described manner so as to equalize the pressure in lines 8 and9 and permit the dragging motor 6 or pump to reach a free-wheeling orneutral or idle position so as not to detract from the eticiency of thefaster running motor connected via clutch 5 with drum 3.

In the opposite direction of rotation, the same freewheeling effect canbe attained by displacing valve 17 to position 21 whereby excesspressure in line 8, now a return iline, may be equalized viashort-circuit line 11 with t'he pressure in line 9 now a working line.

In the event the motor 6 associated via clutch 5 with drum 3 is thedragging motor, then the reverse operation may be carried out bysuitable displacement of the appropriate valve 17 associated with thathydraulic system 7 connected with said motor 6 associated with drum 3.

Advantageously, in accordance with the present invention, check valves12 and 13 are normally maintained in closed position by the positivepressure ow via lines 8 and 9, and each check valve is connectedoperatively with control valve 17 to permit independently opening ofcheck valves 12 and 13 with respect to one another and indeedwithrespect to the existing pressure in either or both of lines 8 or 9. Theconstruction of check valves 12 and 13 is conventional and the operativeconnection of valve 17 therewith to provide independent actuation ofsuch check valves to open the same despite the pressure in lines 8 and 9is also conventional (cf. U.S. Patents 2,467,508 and 3,135,087, andGerman Patent 1,045,202). Of course, any valve means may be utilized asvalves 12 and 13 herein so long as such valves are functionally opposedin operative connection in the short-circuit line or by-pass line 11 andopenable independently of one another by a control system not related tothe hydraulic pressure in line 8 and line 9, yet with each valve 12 and13 being unilaterally operated in the sense that the appropriatepositive pressure directly now-communicated therewith by line 8 or line9, as the case may be, will normally maintain the particular check valve12 or 13 in closed position under the attendant hydraulic pressureexerted thereagainst, yet displaceab-le despite such attendant pressureby independent actuation caused by control means such as control valve17, or the like.

It will be appreciated that more than two such by-pass lines may beprovided in any such hydraulic system 7, each having appropriatelydisposed therein a pair of functionally opposed check valves 12 and 13of the type contemplated with control means operatively connected withboth such check valves to control the opening thereof independently ofthe pressure in the hydraulic system 7. Also, while two motors 6 areshown in the embodiment of the drawing, it will be appreciated that anynumber of motors 6 may be provided in conjoint operative association toproduce an additive resultant power for running a given device, whereinit is desirable to operate such device under rotary |motion of theindividual motors 6 at the same speed in the interests of over-alleciency. By using a system of the type shown, instead of intricategearing arrangements, the reversal of rotation of drums 2 and 3, or thelike, may be achieved by simply changing the direction of workingpressure and return pressure in the hydraulic systems 7 via theappropriate directional operation ofthe pump 10, or the like.

It will be further realized that but one such motor 6 associated with agiven hydraulic system 7 may be provided where it is desired to providerotary motion at a constant speed or at least at a minimum speed for adrivable system. In the case of a lminirnum speed, it will be realizedthat by providing the instant by-p'ass arrangement in the hydraulicsystem 7, motor 6 will not act as a brake under any circumstances sincewhen the speed of the rotary motion through the appropriate clutch 4,for

instance, exceeds that supplied by the corresponding motor 6, instead of'a braking effect, motor 6 will assume a neutral or idle free-runningstate until the speed of motor 6 once more exceeds that through clutch4, whereupon positive rotation of motor 6 will once again be undertaken.This will lbe true since the pressure in the working line 8 will onceagain exceed that in return line 9 so as to cause the closing of checkvalve 12 under the existing pressure in line 8 which is higher than thepressure in line 9 communicating via open check Valve 13 andshortcircuit line 11 with valve 12.

Valve 17 may be in the form of a manually operated valve having thethree stated positions, with springs 23 and 24 normally biasing suchvalve in the neutral or idle position 20, yet which permit in theposition 22 the independent opening of valve 13 and in the position 21the independent opening of valve 12 to achieve the results describedhereinabove, depending upon whether motor 6 is operating in clockwise orcounterclockwise direction and in turn whether the hydraulic pressure inline 8 is meant to exceed normally that in line 9, or vice versa.Additionally, valve 17 may be a magnetically controlled threeway valveof the aforementioned type which may be operated electromagnetically byconventional control systems (not shown) including servo motors, etc.,causing displacement, for example, between the nonmal, neutral or idleposition 20 and, on the one hand, position 21 and, on the other hand,position 22. Such automatic control means may be coupled with thecontrol for operating pump in the desired direction whereby when pump 10operates in a direction causing working pressure in line 8 and returnpressure in line 9, valve 17 will correspondingly assume position 22,and when pump 10 is operated in the reverse manner, valve 17 willautomatically assume the position 21. Of course, hydraulic control meansmay be utilized as well for operating control valve 17 which may againtbe coupled with the control means for operating pump 10 in the givendirection, or other remote control means may be applied to operate valve17 or to operate check valves 12 and 13 independently of one another toopen such check valves in dependence upon the normal disposition ofpressure in line 8 and line 9 and the normal direction of rotation oflmotor 6 associated therewith.

Therefore, by utilizing the by-pass short-circuit flow line in thehydraulic system 7 in accordance with the present invention in which thetwo functionally opposed check valves are normally kept closed, byappropriate independent opening of a given check valve to achieve abalance of hydraulic pressure in lines 8 and 9 of a given hydraulicsystem 7, hydraulic circulation takes place under the pumping force ofmotor 6 through return line 9, short-circuit line 11 including lopencheck Valves 13 Iand 12, and working line 8, whereby approximatemechanical free-wheeling or idle running of motor 6 will be attained tooffset such pumping action and balance the ra-te of rotation of mot-or 6with that associated therewith through clutch 4 or clutch 5, as the casemay be. It will be realized as aforesaid that one or more such by-passshortcircuit lines may be provided with an appropriate control means toopen the check valves thereof independently of one another andindependently of the hydraulic pressure of the system. and it will befurther realized that the present invention is not meant to be limitedto the means and the arrangement herein shown in the specific embodimentof the drawing, but instead also systems operated by otherpressure-fluid medium, such as compressed air, pneumatic drives, or thelike. Indeed, any machine capable of being energized to produce work orpower in mechanical form and operated by pressure-fluid medium in twoopposing resultant rotary directions may be employed in accordance withthe present invention since the crux of the invention is in coupling theworking pressure or fluid pressure to the machine to be energized withthe return pressure or exhaust pressure of such machine whereby toattain under all operating conditions at least a minimum speed ofrotation, be it a result of the pressure energizing in the desireddirection of the uid motor or of freewheeling idle running thereof at ahigher speed than that achievable under the existing working workingpressure due to the mechanical coupling of such motor with means meantto operate at a minimum speed.

Advantageously, the instant invention may be practiced in Huid motorinstallations with very little additional equipment to prevent reliablyand more or less completely those energy losses which have occurredheretofore. In this regard, unnecessary increases in temperature in thepressure iiuid, such as hydraulic liquid, are avoided since the losseswhich have heretofore occurred took the form of dissipated heat whereasat most only very slight losses are entailed where one drive means isovertaken in speed by another in an arrangement of the present type.This is true since a simple pressure medium circulation flow, e.g.hydraulic circulation, is all that takes place in the system by reasonof the by-pass of the present invention, and such circulation will onlylead to negligible temperature increase and heat dissipation loss.

Desirably, a separate control system should be associated with eachdirection of drive of the particular fluid machine. Specifically, aseparate control system should be provided for each of the twocontrarily disposed check valves in the by-pass line of each drive orfluid motor so that the opening of the desired check valve may becarried out independently. Where an automatic control system for theselection of the opening for the correct check valve is concerned, thecontrolling mechanism may be coupled to operate conjointly with thatcontrolling the direction of rotation of the pump 10 or with othercontrolling means which in turn control that control mechanism used fordetermining the direction of rotation of such pump 10, or the like.

In this regard, the reversal of the direction of rotation of the drivemeans or hydraulic motors in the case of traction cable means fordisplacement of a coal planer or other coal winning apparatus is usuallyaccomplished automatically by limit switches which operate when the fullamplitude in the particular direction of the coal planer, or the like,has been attained and reverse operation is necessary to displace suchcoal planer to the opposite end of the mine face area being worked. Theapplication of the present invention to such a system which will permitreverse rotation of the rotary uid machines and/or idle dispositionduring normal operation in one or the other direction will be readilyapparent. On the other hand, where a system such as that contemplatedherein is used with a mining conveyor or the like, the rotary fluidmachines in accordance with the present invention associated therewithwill normally operate in the same direction of rotation and reversal insuch instance will normally be carried out manually since reversaloccurs only infrequently.

Nevertheless, the arrangement of the present invention may be utilizedadvantageously in all cases in which a plurality of the hydraulic drivemeans are employed conjointly to drive a common system thereby and inspecial cases, as aforesaid, it is possible to use the instantarrangement where only a single hydraulic drive means or rotary fluidmachine is contemplated yet where the freewheeling state is foundnecessary under certain conditions, such as where the hydraulic drive'means must avoid acting as a brake for the system driven thereby.

The simplicity of the by-pass circuit of the present inventionrepresents a distinct advantage as well as the freedom frommalfunctioning. Indeed, the conservation of power in operating rotaryuid machines utilizing the instant arrangement is considerable whereasthe modilications necessary to provide the instant arrangement areinexpensive to carry out.

Thus, the crux of the present invention is in providing a pair of checkvalve means in direct series ow relation with each other in ashort-circuit llow line means interconnecting the main working ilow linemeans and the main return ow line means such that one said check valvem'eans is separately exposed via one corresponding portion of theshort-circuit ow line means to the normally existing positive hydraulicvpressure in the working flow line means exerted thereagainst to maintainsuch one check valve means normally closed, and the other said checkvalve means is separately exposed via the other corresponding portion ofthe short-circuit ow means to the normally existing positive hydraulicpressure in said return flow line means exerted thereagainst to maintainsuch other check valve means normally closed, control means beingoperatively connected with the check valve means to open the sameindependently of one another and independently of the existing hydraulicpressure in the main ow line' means and short-circuit llow line, means.In this way when such other check valve means has been opened by thecontrol means against the existing positive pressure in the return owline means to permit such return ilow line means pressure to beflow-communicated therethrough and in turn to be exerted against saidone check valve means, then upon variation of the relative pressures inthe main flow line means such that the existing pressure in the workingow line means is exceeded by the pressure in the return flow line means,such excess return ow line means pressure will open the one check valvemeans to permit direct llow communication through both of the open checkvalve means between the return flow line means and the working flow linemeans to equalize the pressure therebetween until said working ow linemeans pressure exceeds the return ow line means pressure and causes saidone check valve means to close once again.

Naturally, where various constructional parts have been defined in termsof means in the instant specification, such means have been illustratedin the accompanying drawing as specific elements, but in accordance withthe present invention such means contemplate any and all elements usableto achieve the combination of the shortcircuit by-pass arrangement inthe hydraulic system of a rotary fluid machine or the like, and any andall such constructional elements are contemplated herein just as ifprolix enumeration thereof were set forth in detail herein.

It will be appreciated that the instant specification and drawing areset forth by way of illustration and not limitation, and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention which is to be limited only by thescope of the appended claims.

What is claimed is:

1. Hydraulic drive arrangement which comprises hydraulic drive meanshaving main working flow line means and main return ow line meansoperatively ow connected therewith for the hydraulic actuation thereof,shortcircuit flow line means correspondingly interconnecting saidworking and return flow line means to by-pass said drive means, a pairof independently openable operatively opposed check valve means disposedcorrespondingly in said short-circuit ow line means to permit whenopened short-circuit by-pass ow therethrough, and control meansoperatively connected with said check valve means to open said checkvalve means independently of one another.

2. Arangement according to claim 1 wherein said control means includehydraulic control valve means and control ow line means operativelyll-ow connecting said control valve means with said check valve means toopen hydraulically each check valve means independently.

3. Arrangement according to claim 2 wherein said oontrol valve means aremanually operable.

4. Arrangement according to claim 1 wherein at least two separate saidhydraulic drive means are provided in independent operative associationwith a common drivable system to be driven cooperatively thereby, eachsaid drive means having a separate set of said working and return flowline means operatively flow connected therewith and a separate saidshort-circuit ow line means correspondingly interconnecting said workingand return ow line means to by-pass the particular drive means as wellas a pair of said check valve means disposed correspondingly in theparticular short-circuit ilow line means, and said control means beingoperatively connected with said check valve means to open said checkvalve means independently of one another.

5. Arrangement according to claim 4 wherein each said pair of checkvalve means is provided with a separate said control means operableindependently ot the other.

6. Arrangement according to claim 5 wherein said hydraulic drive meansare hydraulically operated rotary drive machines and said commondrivable system is a conveyor system.

7. Arrangement according to claim ll wherein said pair of check valvemeans are in series low relation in said short-circuit ilow line meansand normally maintained closed by the corresponding normally existingpositive hydranlic pressure exerted thereagainst through the appropriatemain ow line means and the corresponding portion of said short-circuitow line means llow communicating therewith.

8. Arrangement according to claim 1 wherein said pair of check valvemeans are in direct series tlow relation with each other in saidshort-circuit flow line means, one said check valve means beingseparately exposed via one corresponding portion of said short-circuittlow means to the normally existing positive hydraulic pressure in saidworking llow line means exterted thereagainst to maintain such one checkvalve means normally closed and the other said check valve means beingseparately exposed via the other corresponding portion of saidshort-circuit ow means to the normally existing positive hydraulicpressure in said return flow line means exerted thereagainst to maintainsuch other check valve means normally closed, said control means beingoperatively connected with said check valve means to open said checkvalve means independently of one another and independently of theexisting hydraulic pressure in said main llow line means and saidshort-circuit ow line means, whereby when said other check valve meanshas been opened by said control means against the existing positivepressure in said return flow line means to permit such return flow linemeans pressure to be flow communicated therethrough and in turn beexerted against said one check valve means, then upon variation of therelative pressures in said main ilow line means such that the existingpressure in said working flow line means is exceeded by the pressure insaid return -ow line means such excess return ow line means pressurewill open said one check valve means to permit direct ilow communicationthrough both of the open check valve means between said return ow linemeans and said working flow line means to equalize the pressuretherebetween until the working tlow line means pressure exceeds thereturn ow line means pressure and causes said one check valve means toclose once again.

9. Arrangement according to claim 8 wherein two separate said hydraulicdrive means are provided in independent operative association with acommon drivable system to be driven cooperatively thereby, each saiddrive means having a separate set of said working and return flow linemeans operatively ow connected therewith and a separate saidshort-circuit ilow line means correspondingly interconnecting saidworking and return ow line means to by-pass the particular drive meansas well as a pair of said check valve means disposed correspondingly inthe particular short-circuit ilow line means and said control meansbeing operatively connected with said check valve means to open saidcheck valve means independently of one another and independently of theexistig hydraulic pressure in each of the corresponding main tlow linemeans and short-circuit ow line means.

10. Arrangement according to claim. 9 wherein said hydraulic drive meansare hydraulically operated rotary drive 1 1 1 2 machines and said comondrivable system is a conveyor FOREIGN PATENTS System 1,045,202 11/1958Germany.

References Cited I UNITED STATES PATENTS 5 EDGAR W. GEOGHEGAN, PrzmaryExammer. 2,467,508 4/ 1949 Trautman 60-52 US Cl- X-R 3,135,087 6/1964Ebert 60-53XR 9116, 437

